Epoxy/thermoplastic photocurable adhesive composition

ABSTRACT

A curable composition comprising a) a curable epoxy resin, a thermoplastic ethylene-vinyl acetate copolymer resin, and an effective amount of a photocatalyst for the curable epoxy resin, wherein the composition is free from hydrocarbon polyolefins and wherein the sum of a) and b) is 100 weight percent.

FIELD OF THE INVENTION

This invention relates to adhesive compositions. More specifically, thisinvention relates to adhesive compositions comprising thermoplasticresins and epoxy resins. The invention also provides a method ofpreparing adhesive compositions and adhesive articles and uses thereof.

BACKGROUND OF THE INVENTION

Adhesive composition blends of curable epoxy resins with variousthermoplastic polymers are known. For example, adhesive compositionscomprising epoxy and polyester thermoplastic resins have been used ashot melt adhesives and in the manufacture of structural bonding andsealing tapes.

However, adhesive compositions consisting of epoxy resins andthermoplastic polyesters have several deficiencies. For example, theycan be prone to excessive flow prior to or during cure, unless flowcontrol additives are incorporated. This excessive flow may result in amessy adhesive bond line that must be smoothed out in a subsequent stepin cases where appearance is important (for example, exterior automotiveapplications such as trim adhesion, body panel and door skinreplacement). Additionally, excessive flow can form gaps in the bondline which may lead to bond failure due to moisture penetration orcorrosion. Also, those epoxy-polyester adhesive compositions that havebeen formulated not to undergo excessive flow typically lack sufficienttack to be used in the form of a thermosettable pressure-sensitive tapewithout incorporation of additional ingredients or a separate adhesivelayer. Further, in order to obtain tack and good adhesion to paintedmetal substrates it is often necessary to increase the epoxy content ofthe adhesive composition above that level which otherwise achievesoptimal properties.

Thermally curable compositions of epoxy resins having ethylene-vinylacetate (also called "EVA" herein) copolymer particles dispersed thereinhave also been disclosed as toughened epoxy resins containing adispersed phase of EVA polymerized in situ.

Epoxy material containing compositions having thermal curatives orhardeners such as those described above are difficult to melt processinto articles (for example, tapes, films, or rods) without causingpremature curing of the composition. Use of high temperature curativesthat do not cause curing during such processing steps requires a highcure temperature during formation of the adhesive bond, which can causeexcessive flow of the adhesive during cure thereby resulting in anaesthetically unpleasant or structurally defective bond or thermaldamage on the case of thermally sensitive substrates.

SUMMARY OF THE INVENTION

The invention provides curable compositions formed by mixing componentscomprising:

a) from about 20 to about 80 weight percent of a curable epoxy resin;

b) from about 20 to about 80 weight percent of a thermoplasticethylene-vinyl acetate copolymer resin; and

c) an effective amount of a photocatalyst for the curable epoxy resinsuch that the total of components a) and b) is 100 percent and, whereinthe compositions are free from hydrocarbon polyolefins and arehomogeneous mixtures.

The compositions of the invention, exclusive of additives, formhomogeneous and single phased molten mixtures and resulting uncuredsolids, for example, unsupported films.

The compositions of the invention may also contain up to 50 percent byvolume, preferably up to 30 percent by volume, of the total compositionof various additives such as fillers, tackifiers, and the like.

In another aspect, the invention describes a method comprising the stepsof:

a) providing a homogeneous molten mixture comprising a curable epoxyresin, a thermoplastic ethylene-vinyl acetate copolymer resin; and aneffective amount of a photocatalyst for the curable epoxy resin, whereinthe composition is free from hydrocarbon polyolefins;

b) applying the mixture to a substrate or processing into an unsupportedfilm; and

c) at any subsequent time, activating the photocatalyst to cure theepoxy containing material.

If necessary, the compositions may be heated to accelerate cure or toensure complete cure.

The present invention overcomes the deficiencies of polyester-epoxy andthermally cured EVA-epoxy adhesives by providing compositions havingsignificant tack in the uncured state, good cured adhesion to surfacetreated (for example, E-coated) metals, low controlled flow duringcuring and desirable physical properties of the cured resin (structuraladhesive and cohesive strength, and paintability). The improved tack ofthe adhesive in the uncured state keeps the adhesive in place duringassembly and minimizes the need for the use of clamps during the curestep. Further, the present invention provides bonding tapescharacterized by good tack, limited mass flow and structural bondstrength (that is, >1000 psi (6.9 mega Pascals (Mpa)) overlap shearstrength) and can be processed on a 100 percent solids basis without theuse of solvents typically used in the art.

The adhesive compositions of the invention are free from, that is, donot contain, hydrocarbon polyolefin resins. "Hydrocarbon polyolefinresin" refers to a fully prepolymerized uncrosslinked polymerichydrocarbon bearing essentially no organic functional groups, preparedfrom homopolymerization and/or copolymerization of an olefinicmonomer(s). Such resins are typically incompatible with epoxy resins andwill cause phase separation of compositions containing an appreciableamount of epoxy resin. Examples of such resins include polyethylene,polypropylene, and the like, and poly(ethylene-co-propylene),poly(propylene-co-1-butene), and the like.

A "tape" is defined as an uncured adhesive film attached to either arelease liner or a backing that can be formed into a roll or cut intopieces and having a length greater than its width.

An "unsupported film" is defined as an uncured adhesive film havingadhesive characteristics that may be tacky or not tacky at ambienttemperature.

A "curable" or "uncured" composition is a composition that remainsthermoplastic and melt processable and substantially uncrosslinked untilsubjected to either heat, light, or a combination of both at which timethe composition polymerizes and/or crosslinks to form a thermosetmaterial.

A "protected film" is an uncured adhesive film having a release liner orbacking attached that can be formed into a roll or cut into pieces andhaving a length that is substantially the same as its width.

DETAILED DESCRIPTION

The adhesive compositions of the invention comprise from about 20 toabout 80, preferably 30 to 70, more preferably 40 to 60 weight percentof an epoxy containing material, from about 20 to about 80, preferablyfrom about 30 to about 70, more preferably from about 40 to about 60,weight percent ethylene-vinyl acetate copolymer, and an effective amountof a photocatalyst for the curable epoxy containing material, the weightpercent being based on the total weight of epoxy resin andethylene-vinyl acetate copolymer, and the compositions are free ofhydrocarbon polyolefin resins.

Epoxy resins useful in the adhesive compositions of the invention areany organic compounds having at least one oxirane ring, that is,##STR1## polymerizable by a ring opening reaction. Such materials,broadly called epoxides, include both monomeric and polymeric epoxidesand can be aliphatic, alicyclic, heterocyclic, cycloaliphatic, oraromatic and can be combinations thereof. They can be liquid or solid orblends thereof, blends being useful in providing tacky adhesive films.These materials generally have, on the average, at least two epoxygroups per molecule and are also called "polyepoxides." The polymericepoxides include linear polymers having terminal epoxy groups (forexample, a diglycidyl ether of a polyoxyalkylene glycol), polymershaving skeletal oxirane units (for example, polybutadiene polyepoxide),and polymers having pendent epoxy groups (for example, a glycidylmethacrylate polymer or copolymer). The molecular weight of the epoxyresin may vary from about 74 to about 100,000 or more. Mixtures ofvarious epoxy resins can also be used in the hot melt compositions ofthe invention. The "average" number of epoxy groups per molecule isdefined as the number of epoxy groups in the epoxy resin divided by thetotal number of epoxy molecules present.

Useful epoxy resins include those which contain cyclohexene oxide groupssuch as the epoxycyclohexane carboxylates, typified by3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate,3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methycyclohexanecarboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate. For amore detailed list of useful epoxides of this nature, reference may bemade to U.S. Pat. No. 3,117,099, incorporated herein by reference.

Further epoxy resins which are particularly useful in the practice ofthis invention include glycidyl ether monomers of the formula: ##STR2##where R' is aliphatic, for example, alkyl, aromatic, for example, aryl,or combinations thereof, and n is an integer of 1 to 6. Examples are theglycidyl ethers of polyhydric phenols obtained by reacting a polyhydricphenol with an excess of chlorohydrin such as epichlorohydrin, forexample, the diglycidyl ether of 2,2-bis-(4-hydroxyphenol)propane(Bisphenol A). Further examples of epoxides of this type which can beused in the practice of this invention are described in U.S. Pat. No.3,018,262, incorporated herein by reference. Preferred epoxy resinsinclude diglycidyl ethers of Bisphenol A and hydrogenated bisphenolA-epichlorohydrin based epoxy resins.

There is a host of commercially available epoxy resins which can be usedin this invention. In particular, epoxides which are readily availableinclude octadecylene oxide, epichlorohydrin, styrene oxide,vinylcyclohexene oxide, glycidol, glycidyl methacrylate, diglycidylether of Bisphenol A (for example, those available under the tradedesignations "EPON 828", "EPON 1004", and "EPON 1001F" from ShellChemical Co., and "DER-332" and "DER-334", from Dow Chemical Co.),diglycidyl ether of Bisphenol F (for example, those under the tradedesignations "ARALDITE GY281" from Ciba-Geigy Corp., and "EPON 862" fromShell Chemical Co.), vinylcyclohexane dioxide (for example, having thetrade designation "ERL-4206" from Union Carbide Corp.),3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexene carboxylate (for example,having the trade designation "ERL-4221" from Union Carbide Corp.),2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy) cyclohexane-metadioxane (forexample, having the trade designation "ERL-4234" from Union CarbideCorp.), bis(3,4-epoxycyclohexyl) adipate (for example, having the tradedesignation "ERL-4299" from Union Carbide Corp.), dipentene dioxide (forexample, having the trade designation "ERL-4269" from Union CarbideCorp.), epoxidized polybutadiene (for example, having the tradedesignation "OXIRON 2001" from FMC Corp.), epoxy silanes, for example,beta-3,4-epoxycyclohexylethyltrimethoxy silane andgamma-glycidoxypropyltrimethoxy silane, commercially available fromUnion Carbide, flame retardant epoxy resins (for example, having thetrade designation "DER-542", a brominated bisphenol type epoxy resinavailable from Dow Chemical Co.), 1,4-butanediol diglycidyl ether (forexample, having the trade designation "ARALDITE RD-2" from Ciba-Geigy),hydrogenated bisphenol A-epichlorohydrin based epoxy resins (for examplehaving the trade designation "EPONEX 1510" from Shell Chemical Co.), andpolyglycidyl ether of phenol-formaldehyde novolak (for example, havingthe trade designation "DEN-431 " and "DEN-438" from Dow Chemical Co.).

Catalysts

Catalysts of the present invention preferably are activated byphotochemical means, such as by actinic radiation (radiation having awavelength in the ultraviolet or visible portion of the electromagneticspectrum). Useful photocatalysts are of two general types: onium saltsand cationic organometallic salts, both described in U.S. Pat. No.5,709,948, incorporated herein by reference.

Onium salt photoinitiators for cationic polymerizations include iodoniumand sulfonium complex salts. Useful aromatic iodonium complex salts areof the general formula: ##STR3## wherein Ar¹ and Ar² can be the same ordifferent and are aromatic groups having from 4 to about 20 carbonatoms, and are selected from the group consisting of phenyl, thienyl,furanyl, and pyrazolyl groups;

Z is selected from the group consisting of oxygen, sulfur, and acarbon--carbon bond, ##STR4## wherein R can be aryl (having from 6 toabout 20 carbon atoms, such as phenyl) or acyl (having from 2 to about20 carbon atoms, such as acetyl, or benzoyl), and ##STR5## wherein R₁and R₂ are selected from the group consisting of hydrogen, alkylradicals having from 1 to about 4 carbon atoms, and alkenyl radicalshaving from 2 to about 4 carbon atoms;

m is zero or 1; and

X has the formula DQ_(n), wherein D is a metal from Groups IB to VIII ora metalloid from Groups IIIA to VA of the Periodic Chart of the Elements(Chemical Abstracts version), Q is a halogen atom, and n is an integerhaving a value of from 1 to 6. Preferably, the metals are copper, zinc,titanium, vanadium, chromium, magnesium, manganese, iron, cobalt, ornickel and the metalloids preferably are boron, aluminum, antimony, tin,arsenic and phosphorous. Preferably, the halogen, Q, is chlorine orfluorine. Illustrative of suitable anions are BF₄ ⁻, PF₆ ⁻, SbF₆ ⁻,FeCl₄ ⁻, SnCl₅ ⁻, AsF₆ ⁻, SbF₅ OH⁻, SbCl₆ ⁻, SbF₅ ⁻², AlF₅ ⁻², GaCl₄ ⁻,InF₄ ⁻, TiF₆ ⁻², ZrF₆ ⁻, CF₃ SO₃ ⁻¹, and the like. Preferably, theanions are BF₄ ⁻, PF₆ ⁻, SbF₆ ⁻, AsF₆ ⁻, SbF₅ OH⁻, and SbCl₆ ⁻. Morepreferably, the anions are SbF₆ ⁻, AsF₆ ⁻, and SbF₅ OH⁻.

The Ar₁ and Ar₂ aromatic groups may optionally comprise one or morefused benzo rings (for example, naphthyl, benzothienyl, dibenzothienyl,benzofuranyl, dibenzofuranyl, etc.). The aromatic groups may also besubstituted, if desired, by one or more non-basic groups if they areessentially non-reactive with epoxide and hydroxyl functionalities.

Useful aromatic iodonium complex salts are described more fully in U.S.Pat. No. 4,256,828, which is incorporated herein by reference. Thepreferred aromatic iodonium complex salts are (Ar)₂ I PF₆ and (Ar)₂ ISbF₆.

The aromatic iodonium complex salts useful in the invention arephotosensitive only in the ultraviolet region of the spectrum. However,they can be sensitized to the near ultraviolet and the visible range ofthe spectrum by sensitizers for known photolyzable organic halogencompounds. Illustrative sensitizers include colored aromatic polycyclichydrocarbons, as described in U.S. Pat. No. 4,250,053, incorporatedherein by reference. Suitable sensitizers should be chosen so as to notinterfere appreciably with the cationic cure of the epoxy resin in theadhesive composition.

Aromatic sulfonium complex salt initiators suitable for use in theinvention are of the general formula: ##STR6## wherein R₃, R₄, and R₅can be the same or different, provided that at least one of the groupsis aromatic. These groups can be selected from the group consisting ofaromatic moieties having from 4 to about 20 carbon atoms (for example,substituted and unsubstituted phenyl, thienyl, and furanyl) and alkylradicals having from 1 to about 20 carbon atoms. The term "alkyl"includes substituted alkyl radicals (for example, substituents such ashalogen, hydroxy, alkoxy, and aryl). Preferably, R₃, R₄, and R₅ are eacharomatic; and

Z, m, and X are all as defined above with regard to the iodonium complexsalts.

If R₃, R₄, or R₅ is an aromatic group, it may optionally have one ormore fused benzo rings (for example, naphthyl, benzothienyl,dibenzothienyl, benzofuranyl, dibenzofuranyl, etc.). The aromatic groupsmay also be substituted, if desired, by one or more non-basic groups ifthey are essentially non-reactive with epoxide and hydroxylfunctionalities.

Triaryl-substituted salts such as triphenylsulfoniumhexafluoroantimonate and p-(phenyl(thiophenyl)diphenylsulfoniumhexafluoroantimonate are the preferred sulfonium salts. Useful sulfoniumsalts are described more fully in U.S. Pat. Nos. 5,256,828 and4,173,476.

Aromatic sulfonium complex salts useful in the invention are typicallyphotosensitive only in the ultraviolet region of the spectrum. However,they can be sensitized to the near ultraviolet and the visible range ofthe spectrum by a select group of sensitizers such as described in U.S.Pat. Nos. 4,256,828 and 4,250,053.

If a sensitizer is used in combination with iodonium or sulfonium saltsas described above, it should be chosen so as to not interfereappreciably with the cationic cure of the epoxy resin in the adhesivecomposition.

Suitable photoactivatable organometallic complex salts useful in theinvention include those described in U.S. Pat. Nos. 5,059,701;5,191,101; and 5,252,694, each of which is incorporated herein byreference. Such salts of organometallic cations have the generalformula:

    [(L.sup.1)(L.sup.2)M.sup.m ].sup.+e X.sup.-

wherein

M^(m) represents a metal atom selected from elements of periodic groupsIVB, VB, VIB, VIIB, and VIII, preferably Cr, Mo, W, Mn, Re, Fe, and Co;

L¹ represents none, one, or two ligands contributing π-electrons thatcan be the same or different ligand selected from the group consistingof substituted and unsubstituted alicyclic and cyclic unsaturatedcompounds and groups and substituted and unsubstituted carbocyclicaromatic and heterocyclic aromatic compounds, each capable ofcontributing two to twelve π-electrons to the valence shell of the metalatom M. Preferably, L¹ is selected from the group consisting ofsubstituted and unsubstituted η³ -allyl, η⁵ -cyclopentadienyl, η⁷-cycloheptatrienyl compounds, and η⁶ -aromatic compounds selected fromthe group consisting of η⁶ -benzene and substituted η⁶ -benzenecompounds (for example, xylenes) and compounds having 2 to 4 fusedrings, each capable of contributing 3 to 8π-electrons to the valenceshell of M^(m) ;

L² represents none or 1 to 3 ligands contributing an even number ofσ-electrons that can be the same or different ligand selected from thegroup consisting of carbon monoxide, nitrosonium, triphenyl phosphine,triphenyl stibine and derivatives of phosphorous, arsenic and antimony,with the proviso that the total electronic charge contributed to M^(m)by L¹ and L² results in a net residual positive charge of e to thecomplex;

e is an integer having a value of 1 or 2, the residual charge of thecomplex cation; and

X is a halogen-containing complex anion, as described above.

Examples of suitable salts of organometallic complex cations useful asphotoactivatable catalysts in the present invention include:

(η⁶ -benzene)(η⁵ -cyclopentadienyl)Fe⁺¹ SbF₆ ⁻

(η⁶ -toluene)(η⁵ -cyclopentadienyl)Fe⁺¹ AsF⁶ ⁻

(η⁶ -xylene)(η⁵ -cyclopentadienyl)Fe⁺¹ SbF₆ ⁻

(η⁶ -cumene)(η⁵ -cyclopentadienyl)Fe⁺¹ PF₆.sup.-

(η⁶ -xylenes (mixed isomers))(η⁵ -cyclopentadienyl)Fe⁺¹ SbF₆ ⁻

(η⁶ -xylenes (mixed isomers))(η⁵ -cyclopentadienyl)Fe⁺¹ PF₆ ⁻

(η⁶ -o-xylene)(η⁵ -cyclopentadienyl)Fe⁺¹ CF₃ SO₃ ⁻

(η⁶ -m-xylene)(η⁵ -cyclopentadienyl)Fe⁺¹ BF₄ ¹

(η⁶ -mesitylene)(η⁵ -cyclopentadienyl)Fe⁺¹ SbF₆ ⁻

(η⁶ -hexamethylbenzene)(η⁵ -cyclopentadienyl)Fe⁺¹ SbF₅ OH⁻ and

(η⁶ -fluorene)(η⁵ -cyclopentadienyl)Fe⁺¹ SbF₆ ⁻.

Preferred salts of organometallic complex cations useful in theinvention include one or more of the following: (η⁶ -xylenes (mixedisomers))(η⁵ -cyclopentadienyl)Fe⁺¹ SbF₆ ⁻, (η⁶ -xylenes (mixedisomers))(η⁵ -cyclopentadienyl)Fe⁺¹ PF₆ ⁻, (η⁶ -xylene)(η⁵-cyclopentadienyl)Fe⁺¹ SbF₆ ⁻, and (η⁶ -mesitylene)(η⁵-cyclopentadienyl)Fe⁺¹ SbF₆ ⁻.

Useful commercially available initiators include FX-512™ (MinnesotaMining and Manufacturing Company, St. Paul, Minn.), CD-1012™, andCD-1010™ (Sartomer, Exton, Pa.) aromatic sulfonium complex salts,UVI™-6974, an aromatic sulfonium complex salt (Union Carbide Corp.,Danbury, Conn.) and IRGACURE™ 261, a cationic organometallic complexsalt (Ciba Geigy Chemicals, Hawthorne, N.Y.).

Preferably, the photocatalyst is present in the compositions of theinvention at levels from about 0.01 to about 10 weight percent, morepreferably from about 0.1 to about 5 weight percent, still morepreferably from about 0.5 to about 2 weight percent, based on the totalweight of the resin (epoxy and EVA) present in the composition.

Where the catalytic photoinitiator used for curing the epoxy resin is ametallocene salt catalyst, it optionally is accompanied by anaccelerator such as an oxalate ester of a tertiary alcohol as describedin U.S. Pat. No. 5,436,063, although this is optional. Oxalateco-catalysts that can be used include those described in U.S. Pat. No.5,252,694. The accelerator comprises from about 0.01 to about 5 weightpercent, preferably from about 0.1 to about 4 weight percent of theadhesive composition based on the combined weight of the epoxy resin andthe thermoplastic ethylene-vinyl acetate copolymer.

Ethylene Vinyl Acetate Copolymer

The thermoplastic component of the invention includes and preferably,consists essentially of one or more thermoplastic ethylene-vinyl acetatecopolymer resins. Useful ethylene-vinyl acetate copolymers of thepresent invention are thermoplastic and contain at least 28 percent byweight vinyl acetate, preferably at least 40 percent by weight vinylacetate, more preferably at least 50 percent by weight vinyl acetate,and even more preferably at least 60 percent by weight vinyl acetate byweight of the copolymer. Useful ranges of vinyl acetate weight percentsinclude from 28 to 99, generally from 40 to 90, preferably from 50 to90, and more preferably from 60 to 80 weight percent vinyl acetate inthe copolymer. The useful ethylene-vinyl acetate copolymers may containup to 99 percent by weight vinyl acetate.

Non-limiting examples of commercially available ethylene-vinyl acetatecopolymers that may used in practice of the present invention includeELVAX™ 210, 250, 260, and 265 (E. I. Du Pont de Nemours and Co.,Wilmington, Del.), and AT Plastics 2820M EVA copolymer (AT Plastics,Inc., Brampton, Ontario, Canada) (28 weight percent vinyl acetate);ELVAX™ 150 and AT Plastics 3325M EVA copolymer (33 weight percent vinylacetate); ELVAX™ 40W and LEVAPREN™ 400 (Bayer Corp., Pittsburgh, Pa.),AT Plastics 4030M (40 weight percent vinyl acetate); LEVAPREN™ 450, 452,and 456 (45 weight percent vinyl acetate; LEVAPREN™ 500HV (50 weightpercent vinyl acetate), LEVAPREN™ 600 HV (60 weight percent vinylacetate); LEVAPREN™ 700 HV (70 weight percent vinyl acetate); LEVAPREN™KA 8479 (80 weight percent vinyl acetate), and the like.

The components used to form the adhesive compositions of the inventionare compatible in the molten state. "Compatible" means that the moltenmixture of at least the epoxy and thermoplastic components is singlephased, that is, does not visibly phase separate among the individualcomponents and forms a homogeneous molten and resulting solid mixture.Of course, one skilled in the art can easily vary the concentrations ofthe epoxy resins, EVA copolymers and vinyl acetate content therein, andcatalysts to form compositions of the invention without undueexperimentation. For example, one skilled in the art would generallyincrease the vinyl acetate concentration of the EVA copolymer as theconcentration epoxy containing material in the composition increases soto maintain a singled phased composition in the molten state.

The specific physical properties of the cured adhesive may also betailored to suit the specific application by adjusting the ratio of thepreceding components. Generally, increased tack and adhesion to highenergy surfaces, and a decreased tendency to flow during cure isachieved by increasing the relative amount of EVA copolymer in theformulation. Additionally, tack of the composition may be affected bythe amount of plasticization of the EVA copolymer by a liquid epoxyresin. The amount of photocatalyst is selected to optimize cure speedand uniformity of through cure. Thus, the relative amounts of theabove-mentioned ingredients are balanced depending on the propertiessought in the final composition.

Hydroxyl Containing Material

Optionally, the adhesive compositions of the invention may furthercomprise a hydroxyl-containing material. The hydroxyl-containingmaterial may be any liquid or solid organic material having hydroxylfunctionality of at least 1, preferably at least 2. Thehydroxyl-containing organic material should be free of other "activehydrogen" containing groups such as amino and mercapto moieties. Thehydroxyl-containing organic material should also preferably be devoid ofgroups which may be thermally or photochemically unstable so that thematerial will not decompose or liberate volatile components attemperatures below about 100° C. or when exposed to the energy sourceduring curing. Preferably the organic material contains two or moreprimary or secondary aliphatic hydroxyl groups (that is, the hydroxylgroup is bonded directly to a non-aromatic carbon atom). The hydroxylgroup may be terminally situated, or may be pendant from a polymer orcopolymer. The number average equivalent weight of thehydroxyl-containing material is preferably about 31 to 2250, morepreferably about 80 to 1000, and most preferably about 80 to 350. Morepreferably, polyoxyalkylene glycols and triols are used as thehydroxyl-containing material. Even more preferably, cyclohexanedimethanol is used as the hydroxyl-containing material.

Representative examples of suitable organic materials having a hydroxylfunctionality of 1 include alkanols, monoalkyl ethers of polyoxyalkyleneglycols, and monoalkyl ethers of alkylene glycols.

Representative examples of useful monomeric polyhydroxy organicmaterials include alkylene glycols (for example, 1,2-ethanediol,1,3-propanediol, 1,4-butanediol, 2-ethyl-1,6-hexanediol, 1,4-cyclohexanedimethanol, 1,18-dihydroxyoctadecane, and 3-chloro-1,2-propanediol),polyhydroxyalkanes (for example, glycerine, trimethylolpropane,pentaerythritol, and sorbitol) and other polyhydroxy compounds such asN,N-bis(hydroxyethyl)benzamide, butane-1,4-diol, castor oil, and thelike.

Representative examples of useful polymeric hydroxyl-containingmaterials include polyoxyalkylene polyols (for example, polyoxyethyleneand polyoxypropylene glycols and triols of equivalent weight of 31 to2250 for the diols or 80 to 350 for triols), polytetra-methylene oxideglycols of varying molecular weight, hydroxyl-terminated polyesters, andhydroxyl-terminated polylactones.

Useful commercially available hydroxyl-containing materials includethose described in U.S. Pat. No. 5,436,063, incorporated herein byreference.

The amount of hydroxyl-containing organic material used in thecompositions of the invention may vary over a broad range, depending onfactors such as the compatibility of the hydroxyl-containing materialwith both the epoxy resin and the ethylene-vinyl acetate copolymercomponent, the equivalent weight and functionality of thehydroxyl-containing material, and the physical properties desired in thefinal cured adhesive composition. Typically, the amount of hydroxylcontaining material in compositions of the invention range from 0 toabout 25 percent by weight of the epoxy containing material in thecomposition.

The optional hydroxyl-containing material is particularly useful intailoring the glass transition temperature and flexibility of thecompositions of the invention. As the equivalent weight of thehydroxyl-containing material increases, the flexibility of the hot meltmake coat correspondingly increases although there may be a consequentloss in cohesive strength. Similarly, decreasing equivalent weight mayresult in a loss of flexibility with a consequent increase in cohesivestrength. Thus, the equivalent weight of the hydroxyl-containingmaterial is selected so as to balance these two properties.

As explained more fully hereinbelow, the incorporation of hydroxylcontaining materials, specifically polyether polyols, into thecompositions of the invention is especially desirable for adjusting therate at which the adhesive compositions cure upon exposure to energy.Useful polyether polyols (that is, polyoxyalkylene polyols) foradjusting the rate of cure include polyoxyethylene and polyoxypropyleneglycols and triols having an equivalent weight of about 31 to 2250 forthe diols and about 80 to 350 for the triols, as well aspolytetramethylene oxide glycols of varying molecular weight andpolyoxyalkylated bisphenol A's.

The relative amount of the optional hydroxyl-containing organic materialis determined with reference to the ratio of the number of hydroxylgroups to the number of epoxy groups in the composition. That ratio mayrange from 0:1 to 1:1, more preferably from about 0.4:1 to 0.8:1. Largeramounts of the hydroxyl-containing material increase the flexibility ofthe composition but with a consequent loss of cohesive strength. If thehydroxyl containing material is a polyether polyol, increasing amountswill further slow the curing process.

Additives

Optionally, the adhesive compositions of the invention further compriseup to about 50 percent, preferably, up to 30 percent, by total volume ofvarious additives such as fillers, stabilizers, plasticizers,tackifiers, flow control agents, cure rate retarders, adhesion promoters(for example, silanes and titanates), adjuvants, additives, and thelike, such as silica, glass, clay, talc, pigments, colorants, glassbeads or bubbles, glass or ceramic fibers, antioxidants, and the like,so as to reduce the weight or cost of the composition, adjust viscosity,and provide additional reinforcement or modify the thermal conductivityof the adhesives compositions and articles of the invention so that amore rapid or uniform cure may be achieved.

Adhesive compositions of the invention may be made electricallyconductive, or their resistivity can be lowered to a desired level bythe inclusion of electrically conductive filler agents. Such materialsinclude metals, metal-alloys, graphite, etc. in forms such as particles,spheres, flakes, fibers, whiskers, wovens, or non-wovens. Polymeric,ceramic, glass, or other non-conductive materials in the above formsthat have an electrically-conductive coating or layer, or that are dopedwith salts or electrolytes may also be useful fillers for this purpose.Intrinsically conductive organic polymers or other materials may also beused. The choice of filler type, shape, volume percentage loading, etc.can be made according to known methods in order to render the adhesivefilm isotropically conductive or anistropically (z-axis) conductivedepending on the intended application.

Some of the materials above also exhibit useful thermal conductivity andcan be used in appropriate quantities to render films of the inventionthermally conductive. Or, where it is desired that the film be thermallyconductive but electrically insulating, useful fillers include ceramicssuch as aluminum oxide, glass, boron nitride, zinc oxide, andnon-ceramics such as diamond. These materials may be used in the some ofthe same forms as those listed above for electrically conductivematerials.

The various additives are not included in the foregoing weight percentcalculations for the adhesive composition.

Method of Making

The adhesive compositions of the invention can be prepared by usingeither a batch or a continuous process as long as the components arecompatible in the melt phase, that is, no visible phase separation amongthe components.

In a batch process, the adhesive compositions of the invention areprepared by mixing the various ingredients in a suitable vessel,preferably one that is not transparent to actinic radiation, at anelevated temperature sufficient to liquefy the components so that theycan be efficiently mixed with stirring until the components arethoroughly melt blended but without thermally degrading or causingpremature curing of the materials. The components may be addedsimultaneously or sequentially, although it is preferred to first blend(in order) the ethylene-vinyl acetate copolymer and epoxy-containingmaterial and followed by the addition of the photocatalyst for the epoxycontaining material.

In a continuous process, the adhesive compositions of the invention aremixed in an extruder as above, for example a twin screw extruder,equipped with a down stream port, a static mixer, and an appropriateoutput orifice (film die, sheet die, profile die, etc.) and a take-uproll and wind up roll(s), as appropriate. Take-up line speed is adjustedas appropriate for the output form.

Compositions may be used directly after melt blending (in a molten form)or may be packaged as a solvent free system in pails, drums, cartridgesor other suitable containers, preferably in the absence of light, untilready for use. The compositions so packaged may be delivered to ahot-melt applicator system with the use of pail unloaders, cartridgedispensers, and the like. Alternatively, the adhesive compositions ofthe invention may be delivered to conventional bulk hot melt applicatorand dispenser systems in the form of sticks, pellets, slugs, blocks,pillows or billets for use in continuous processes.

It is also possible to provide the adhesive compositions of theinvention as uncured, unsupported adhesive films. Such films are usefulin laminating operations and are preferably not tacky.

If the adhesive composition is tacky, it may be provided as a tape,wherein the adhesive composition is provided in film or layer form androlled up into a roll with a release liner (for example, silicone-coatedKraft paper), with subsequent packaging in a bag or other container thatis not transparent to actinic radiation.

Use

The molten adhesive compositions of the invention may be applied to awide variety of substrates by extruding, spraying, gravure printing, orcoating, (for example, by using a coating die, a heated knife bladecoater, a roll coater or a reverse roll coater). Alternatively, theadhesive composition may be applied to a substrate in the form of anuncured adhesive film which, if necessary, can be die cut to apredefined shape. Once applied, the adhesive film composition may betacky or tack-free, a blend of liquid and solid epoxy-containingmaterials being useful in achieving the former state.

Substrates which can be coated or bonded using compositions of theinvention include plastics, metals, ceramics, glass and cellulosicmaterials although primed, bare, or painted metal substrates such asaluminum, cold rolled steel and porcelainized steel are particularlypreferred.

Curing of the adhesive composition begins upon exposure of thecomposition to any source emitting actinic radiation (that is, radiationhaving a wavelength in the ultraviolet or visible spectral regions) andcontinues for a period of time thereafter. Suitable sources of radiationinclude mercury, xenon, carbon arc, tungsten filament lamps, sunlight,etc. Ultraviolet radiation, especially from a medium pressure mercuryarc lamp, is most preferred. Exposure times may be from less than about1 second to 10 minutes or more (to provide a total energy exposure ofabout 800 milliJoules/square centimeter (mJ/cm²)) for onium saltcatalysts depending upon both the amount and the type of reactantsinvolved, the radiation source, the distance from the radiation source,and the thickness of the composition to be cured. The rate of curingtends to increase with increasing amounts of photoinitiator at a givenlight exposure or irradiation. The rate of curing also increases withincreased radiation intensity.

Those adhesive compositions that include a polyether polyol that retardsthe curing rate, are particularly desirable when bonding together twosubstrates that are not transparent to the radiation. After applying theadhesive composition to the first substrate and irradiating thecomposition, the second substrate may be bonded to the first substratefor a certain period of time (for example, from about 2 minutes to about4 hours) until the composition has sufficiently cured that a useful bondcan no longer be made. Thus, it will be recognized that the presence ofthe polyether polyol provides the adhesive compositions with an opentime. That is, for a period of time (the open time) after thecomposition has been irradiated, it remains sufficiently uncured for asecond substrate to be bonded thereto. The adhesive compositions of theinvention which do not include a polyether polyol may be applied to asingle substrate and irradiated to provide an adhesive coating on thesubstrate.

The second substrate is typically bonded using heat, pressure or bothheat and pressure, (for example, with a heated press, heated niprollers, or a heated laminator). Depending on the particular adhesivecomposition, the conditions for applying the second substrate may rangefrom a few seconds at 177° C. to about 15 seconds at room temperature.Typical exposures are for about 10 seconds at 138° C. Laminatorpressures of about 274 kiloPascals (kPa) are useful. In anotherapproach, for example, when cationic organometallic catalysts are used,a free standing film may be irradiated on one or both sides and thenplaced between two substrates followed by the use of heat, pressure orboth heat and pressure to bond the film to the two substrates.

Alternatively, two substrates may be bonded together if one of thesubstrates is transparent to the radiation, thereby permitting theadhesive composition to be irradiated through the transparent substrate.

Once the adhesive composition is exposed to radiation, the curingprocess is initiated. Subsequent to radiation exposure the adhesivecompositions can be tack-free, or can be tacky for a limited period oftime but eventually achieving a tack-free condition. Full cure may beachieved under ambient conditions in about 24 hours or as little asabout 8 to 16 hours, depending upon the intensity of the radiationsource, the radiation exposure time, the concentration of thephotoinitiator, and the particular ingredients which comprise theadhesive composition.

The time to reach full cure may be accelerated by post curing thecompositions with heat, such as in an oven. The time and temperature ofthe post cure will vary depending upon the concentration and type of thephotoinitiator, the radiation exposure conditions, and the like. Typicalpost cure conditions for onium salt type catalysts range from 5 to 15minutes at about 50° C. to about 1 to 2 minutes at temperatures up toabout 100° C. A typical post cure condition for cationic organometalliccatalysts is from about 15-35 minutes at a temperature of about 177° C.An accelerated cure can also be achieved by applying heat and pressureto bond two substrates together such as when using a heated press, aheated laminator or heated nip rollers.

Articles

Adhesive articles according to the invention may be readily prepared inmany ways. For example, the ingredients for the adhesive composition maybe melted and stirred in a suitable mixing vessel (for example, a batchmixer, an extruder, etc.) at an elevated temperature low enough to avoiddecomposing any photocatalyst present in the adhesive composition. Aftermixing, the adhesive composition may be formed into its final shape by avariety of different methods. For example, the adhesive composition canbe coated onto a release liner to form a tape using a heated knifecoater. Alternatively, the adhesive composition ingredients may becompounded in an extruder and then extruded through a die having adesired profile to produce a shaped strip of adhesive; that is, a striphaving the desired cross-sectional shape.

In another approach, the composition can be extruded as a mass anddelivered between a pair of motor-driven chilled rolls spaced apart apredetermined distance to form a flat sheet of the adhesive compositionthat may be subsequently calendared to the desired thickness.

A structure can be imparted to a major surface of the adhesive layer byextruding the adhesive sheet between a pair of nip rolls, at least oneof which is embossed with the desired pattern. A sheet of the adhesivecomposition can also be embossed at any subsequent time by heating thesheet (if necessary) and pressing the sheet with an embossing roll(which may be heated or unheated) carrying the desired pattern.

In one preferred method of manufacture, an actinic radiation blockingrelease liner is laminated to a film of the uncured adhesive compositionto protect the exposed surfaces of the uncured adhesive film frompremature exposure to actinic radiation and then converted into thedesired final form, (that is, tape, or protected film). This can beaccomplished by, for example, slitting it to the desired width, andwinding it up into roll form and around a suitable plastic or paper coreif needed. Alternatively, the tape or protected film can be slit orotherwise cut into discrete lengths or die cut into desired shapes. Ofcourse, an article can also be prepared by laminating or attaching anytype of backing, for example, cloth, polymer, nonwoven, etc., to theadhesive film of the invention.

It is also necessary to protect the composition from prematureactivation, for example, during storage and shipping. When in the formof protected films, unsupported films, or tapes, this may beaccomplished, for example, by storing the entire tape-bearingconstruction in a radiation-blocking container. The invention will nowbe described further by way of the following non-limiting examples.

EXAMPLES

Unless otherwise specified the materials used in these examples may beobtained from standard commercial sources such as Aldrich Chemical Co.of Milwaukee, Wis. All amounts used in the examples are in parts byweight unless otherwise specified.

Ar₃ S⁺ SbF₆ ⁻ photocurative was prepared as described in U.S. Pat. No.4,173,476 (col. 5, line 43 to col. 6 line 32), incorporated herein byreference.

AT 4030 thermoplastic ethylene-vinyl acetate copolymer resin (55 meltindex, 40 percent vinyl acetate) was obtained from AT Plastics, Inc.(Brampton, Ontario, Canada).

The Brabender mixer was obtained from C. W. Brabender Instruments, Inc.(South Hackensack, N.J.).

Cp(Xylenes)Fe⁺ SbF₆ ⁻ photocurative also described as: (eta⁶-xylenes)(eta⁵ -cyclopentadienyl)iron (1+) hexafluoroantimonate orCpXylFe⁺ SbF₆ ⁻ (Cp=cyclopentadiene) was prepared as disclosed in U.S.Pat. No. 5,089,536 (Palazzotto), incorporated herein by reference.

Overlap shear adhesion values were measured using a SINTECH™ 10 tensiletest system available from MTS Systems Corp. (Research Triangle Park,N.C.).

Super diazo TLD 15W/03 bulbs are available from Philips N.V., TheNetherlands.

E-coated steel panels (ED 5100, ED 5000) were obtained from AdvancedCoating Technologies, Inc. (Hillsdale, Mich.).

ELVAX™ 500W (2500 melt index, 14 percent vinyl acetate) and ELVAX™ 40W(56 melt index, 40 percent vinyl acetate) thermoplastic ethylene-vinylacetate copolymer resins were obtained from E.I. Du Pont de Nemours &Co. (Wilmington, Del.).

EPON™ 1001 F epoxy resin of Bisphenol A (solid at RT), EPON™ 828 epoxyresin of Bisphenol A, and EPONEX™ 1510 hydrogenated BisphenolA-epichlorohydrin based epoxy resin were obtained from Shell ChemicalCo. (Houston, Tex.).

Dicyandiamide (AMICURE™ CG-1200) and CUREZOL™ 2MZ-Azine2,4-diamino-6(2'methylimidazoleyl-(1'))ethyl-s-triazine (thermal curingagents) were obtained from Air Products and Chemicals, Inc. (Allentown,Pa.).

DYNAPOL™ S 1402 (high molecular weight thermoplastic polyester with lowcrystallinity) was obtained from Creanova, Inc. (Somerset, N.J.).

The Fusion Systems LC-6 Benchtop Conveyor and F300 Lamp System wereobtained from Fusion Systems Corp. (Rockville, Md.).

LEVAPREN™ 600HV (Mooney viscosity [ASTM D 1646]=27, 60 percent vinylacetate), LEVAPREN™ 700HV (Mooney viscosity [ASTM D 1646]=27, 70 percentvinyl acetate), LEVAPREN™ 500HV (Mooney viscosity [ASTM D 1646]=27, 50percent vinyl acetate), and LEVAPREN™ 400HV (Mooney viscosity [ASTM D1646]=20, 40 percent vinyl acetate) thermoplastic ethylene-vinyl acetatecopolymer resins were obtained from Bayer Corp. (Pittsburgh, Pa.).

UNILIN™ 425 wax was obtained from Petrolite Corp. (St. Louis, Mo.).

FPL etched metal coupons were freshly prepared according to the etchingprocess described in H. W. Eichner, Forest Products Laboratory; ReportNo. 1842, Apr. 1, 1954, Madison, Wis.

Specifically, the specimens were treated as follows: Each specimen wasdegreased by soaking for 10 minutes in 75 g of OAKITE 164 (alkalinedetergent, Oakite Products Inc. of Berkely Heights, N.J.) per liter ofdistilled water. Each specimen was then rinsed for 2 minutes in tapwater, followed by immersion for 10 minutes at 66-71° C. in an etchingbath consisting of 1161 g of H₂ SO₄, 156.8 g of Na₂ Cr₂ O₇.2H₂ O, 1.5 gof 2024-T3 bare aluminum alloy chips, and enough distilled water to make3.5 liters of solution. Following immersion in the etching solution,each specimen is rinsed for 2 minutes with tap water, air dried for 10minutes, and dried for 10 minutes at 71° C.

General Procedure A for the Preparation of Adhesives

All ingredients other than catalysts were placed in a container andheated in a convection oven to a temperature sufficient to allow mixingby hand. Typically this was at 149° C. for about 60 minutes. Afterremoval from the oven, the samples were mixed by hand using a tonguedepressor. The material was allowed to cool for at least 1 hour beforeproceeding to the next step.

The cooled material was reheated in a convection oven at 121° C. for 90minutes. The sample was then removed from the oven and the catalysts tobe used were added and mixed into the material by hand. The compositionwas reheated if needed to facilitate mixing of the catalysts. Aftermixing, the material was coated immediately onto silicone coated releaseliner or the desired substrate to the desired thickness using a knifecoater with an appropriate coating gap setting.

General Procedure B for the Preparation of Adhesives

Adhesive compositions were prepared in batch mode using a heated,internally-stirred BRABENDER mixer equipped with roller blades operatedat approximately 50 rpm. EVA copolymer was added to the mixer withstirring and heating to 90° C. until homogeneous. The temperature of themixture was observed to increase to approximately 95° C. due to stirringfriction. The epoxy resin was then added slowly and stirring wascontinued for 1 minute. Then remaining ingredients were added such thatany catalysts were added last and stirring was continued until dispersed(ambient light was minimized when photocatalysts were added). Themixture was removed from the reactor and pressed twice at between121-177° C. in a heated laboratory press, between silicone coatedrelease liners to obtain a free-standing film of desired thickness.

Curing of the Adhesive Compositions

Curing of the adhesive compositions of the invention was accomplished asfollows:

CpXylFe⁺ SbF₆ ⁻ containing adhesive compositions were exposed toirradiation using super diazo lamps (TLD 15W/03 lamps, available fromPhillips N.V., Holland) at approximately 2.2 J/cm² for, for example,2-10 minutes depending on the thickness of the film, typically 10minutes per side for 40 mil thickness film at a distance ofapproximately 10 cm. Over exposure to the lights was not detrimental tothe performance of the adhesive.

Ar₃ S SbF₆ ⁻ containing adhesive compositions were exposed, bonded, andcured in the following manner. Samples were pressed into films betweensilicone coated polyester release liners and cut to the appropriatesize, usually 1.27 cm×2.54 cm, and the release liner was removed fromone side. The sample was attached to an aluminum plate using a loop oftape sticking to the remaining release liner to prevent the sample frommoving as it passed under the lamp. The sample was exposed using aFUSION SYSTEMS™ LC-6 Benchtop Conveyor with a F300 Lamp System with 118W/cm of lamp power using an "H" Bulb. The conveyor was set at 22 fpm(6.7 m/min), and the dosage was 825 mJ/cm².

Regardless of the exposure method used, the sample was then attached toa 2.54 cm×10.2 cm FPL etched aluminum coupon, the remaining releaseliner was removed, and the sample was exposed again on this side underthe same conditions. Another etched coupon was attached completing theOverlap Shear Test bond specimen. The samples were then postbaked at177° C. for 30 minutes to ensure complete cure.

Test Methods

45° Flow Test

An E-coated panel was cleaned by spraying it with acetone and wiping itdry, allowing sufficient time to ensure complete drying. The sample tobe measured (typically 14.5 mm by 25.4 mm) was lightly adhered to anE-coated panel so that the narrow edge of the sample was pointing downthe panel. The panel was then placed in an oven at a 45° incline for 12minutes at 177° C. unless otherwise specified. The sample was thenremoved from the oven and allowed to cool to room temperature. Flow wasmeasured as the distance (in mm) the sample flowed relative to itsinitial position.

Overlap Shear Test

An adhesive composition was laminated between FPL etched 2024 T3aluminum coupons both 25.4 mm by 76.2 as follows: a 12.7 mm by 25.4 mmsample of adhesive was attached flush to the narrow edge of both couponsso that the overall construction was about 63.5 mm in length. Thelaminate was clamped together with spring-steel binder clips (0.95 cmcapacity clips, ACCO USA, Inc. of Wheeling, Ill.) heated in an oven at177° C. for 20 minutes, unless otherwise specified.

Overlap shear was measured using a SINTECH™ Model 10 tensile testerequipped with a 22.2 kN load cell at a crosshead speed of 2.54 mm/min.The maximum force before breakage of the sample and the failure mode(for example, cohesive, adhesive, mixed) were noted.

Example 1

These examples demonstrate the advantage of using a photocatalyst tocure epoxy-EVA adhesive compositions according to the present invention.The examples were prepared according to General Procedure B.

                                      TABLE 1                                     __________________________________________________________________________              Comparative                                                                          Comparative    Comparative                                     Ingredients Example 1 Example 2 Example 1 Example 3                         __________________________________________________________________________    DYNAPOL ™                                                                            25     25      0      0                                               S1402 r                                                                       LEVAPREN ™ 0 0 25 25                                                       700HV                                                                         EPON ™ 828 25 25 25 25                                                     CpXylFe.sup.+ SbF.sub.6 .sup.- 0.5 0 0.5 0                                    Dicyandiamide 0 1.75 0 1.75                                                   CURAZOL ™ 0 0.75 0 0.75                                                    2-MZ                                                                          45° Flow Test 7 248 0 1                                                (mm)                                                                          Overlap Shear 22.4 +/- 3.7 16.7 +/- 0.5 24.1 +/- 1.5 5.2 +/- 0.2                                             Strength                                       (MPa)                                                                       __________________________________________________________________________

In the case of epoxy-polyester adhesive compositions, only a minordifference in overlap shear performance was observed on substitution ofa photocatalyst for the thermal catalyst. The effect was much larger(approximately 500 percent improvement) in the case of epoxy-EVAadhesive compositions. Further, the overall performance of the epoxy-EVAadhesive compositions changed from lower to higher adhesion values.

Examples 2-7

These examples demonstrate the effect of the EVA/epoxy resin weightratios on the performance properties of adhesive compositions accordingto the present invention. The examples were prepared according toGeneral Procedure A, except for Example 3, which was prepared usingGeneral Procedure B. Example 3 was pressed into a film between siliconecoated polyester liners and Examples 2, 4-7 were coated onto a siliconecoated release liner using a hot knife coater. The samples were cured asdescribed above under the heading "Curing of the Adhesive Compositions."

Examples 2 and 4-7 illustrate the effect of increasing the ratio of EVAto epoxy. Example 3 illustrates the use of a blend of EVA resins incombination with epoxy resin and a photocatalyst.

                  TABLE 2                                                         ______________________________________                                        Ingredients       Example 2                                                                              Example 3                                          ______________________________________                                        LEVAPREN ™ 700HV                                                                             20.0     44.5                                                 (70% vinyl acetate)                                                           LEVAPREN ™ 600HV 0 0                                                       (60% vinyl acetate)                                                           AT 4030 0 10                                                                  (40% vinyl acetate)                                                           EPON ™ 828 79.5 44.5                                                       CpXylFe.sup.+ SbF.sub.6 .sup.- 0.5 1.0                                        Overlap Shear Strength (MPa) 18.6 25.3                                      ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                                     Example  Example  Example                                                                              Example                                   Ingredients 4 5 6 7                                                         ______________________________________                                        LEVAPREN ™ 700HV                                                                        30       40       50     59.5                                      (70% vinyl acetate)                                                           LEVAPREN ™ 600HV 0 0 0 0                                                   (60% vinyl acetate)                                                           AT 4030 0 0 0 0                                                               (40% vinyl acetate)                                                           EPON ™ 828 epoxy 69.5 59.5 49.5 40                                         resin                                                                         CpXylFe.sup.+ SbF.sub.6 .sup.- 0.5 0.5 0.5 0.5                                Overlap Shear Strength 26.7 28.4 26.2 9.3                                     (MPa)                                                                       ______________________________________                                    

Examples 8-10

These examples demonstrate the effect of vinyl acetate content of theEVA copolymer on the compatibility between the EVA copolymer and apreferred epoxy resin. The data show that as the vinyl acetate contentof the EVA copolymer decreases, the incompatibility of the adhesivemixture increases, as demonstrated by lower overlap shear adhesionvalues. Examples 8 and 9 were prepared according to General Procedure A;Example 10 and Comparative Example 4 were prepared according to GeneralProcedure B so as to facilitate mixing.

                  TABLE 3                                                         ______________________________________                                                                            Comparative                                 Ingredients Example 8 Example 9 Example 10 Example 4                        ______________________________________                                        LEVAPREN ™                                                                           49.5     0        0       0                                           700HV                                                                         (70% vinyl                                                                    acetate)                                                                      LEVAPREN ™ 0 49.5 0 0                                                      600HV                                                                         (60% vinyl                                                                    acetate)                                                                      LEVAPREN ™ 0 0 49.5 0                                                      500HV                                                                         (50% vinyl                                                                    acetate)                                                                      LEVAPREN ™ 0 0 0 49.5                                                      400HV                                                                         (40% vinyl                                                                    acetate)                                                                      EPON ™ 828 49.5 49.5 49.5 49.5                                             CpXylFe.sup.+ SbF.sub.6 .sup.- 1.0 1.0 1.0 1.0                                Overlap Shear 26.2 16.7 14.6 Incompatible                                     Strength (MPa)    mixture, could                                                  not be mixed                                                            ______________________________________                                    

Examples 11-13

These examples demonstrate the effect of blends of epoxy and EVA oncompositional compatibility according to the present invention. Examples11 and 12 show the effect of blending relatively high and low vinylacetate-containing EVA copolymers with aromatic and aliphatic epoxyresins. Example 13 is an adhesive made using a relatively low vinylacetate containing EVA copolymer with a blend of aromatic and aliphaticepoxy resins. The above examples were prepared according to GeneralProcedure A.

                  TABLE 4                                                         ______________________________________                                        Ingredients  Example 11 Example 12                                                                              Example 13                                  ______________________________________                                        LEVAPREN ™ 700HV                                                                        25         39.5      0                                             AT 4030 24.5 20 49                                                            EPON ™ 828 25 39.5 20                                                      EPONEX ™ 1510 24.5 0 30                                                    CpXylFe.sup.+ SbF.sub.6 .sup.- 1 1 1                                          Overlap Shear Strength 12.9 17.6 8.8                                          (MPa)                                                                       ______________________________________                                    

Examples 14-17

Examples 14-17 further show the variety of components that may be usedin the adhesive compositions of the invention and their effect on thebond strength of the resulting adhesive. Example 14 contains relativelyhigh vinyl acetate-containing EVA copolymer with an aromatic epoxy and asulfonium catalyst. Examples 15-17 contain epoxy resin that is a solidat room temperature. The examples were prepared according to GeneralProcedure B.

                  TABLE 5                                                         ______________________________________                                                  Example                                                               Ingredients 14 Example 15 Example 16 Example 17                             ______________________________________                                        LEVAPREN ™                                                                           49.5     49        49      39                                         EPON ™ 828 49.5 40 30 40                                                   EPON ™ 1001 0 10 20 20                                                     CpXylFe.sup.+ SbF.sub.6 .sup.- 0 1 1 1                                        Ar.sub.3 S.sup.+ SbF.sub.6 .sup.- 1 0 0 0                                     Overlap Shear 12.5 22.3 23.3 22.7                                             Strength                                                                      (MPa)                                                                       ______________________________________                                    

Examples 18 and 19

These examples illustrate the effect of the vinyl acetate content of anEVA copolymer on the bond strength of an adhesive comprising analiphatic epoxy resin and an EVA copolymer. The examples were preparedaccording to General Procedure A.

                  TABLE 6                                                         ______________________________________                                        Ingredients      Example 18                                                                              Example 19                                         ______________________________________                                        ELVAX ™ 40W   50        0                                                    (40% vinyl acetate)                                                           LEVAPREN ™ 700HV 0 50                                                      (70% vinyl acetate)                                                           EPONEX ™ 1510 50 50                                                        CpXylFe.sup.+ SbF.sub.6 .sup.- 1 1                                            Overlap Shear Strength 7.0 13.2                                               (MPa)                                                                       ______________________________________                                    

Example 20

This example demonstrates an adhesive composition of the presentinvention that is suitable for hem flange bonding. The resultingadhesive had good tack, repositionability, and adhesive performance. Theexample was prepared according to General Procedure B.

                  TABLE 7                                                         ______________________________________                                                          Parts by                                                      Ingredient Weight                                                           ______________________________________                                        LEVAPREN ™ 700HV                                                                             42                                                            EPON ™ 828 31.5                                                            EPON ™ 1001 10.5                                                           Aluminum oxide 15                                                             CpXylFe.sup.+ SbF.sub.6 .sup.- 1                                            ______________________________________                                    

Example 21

This example illustrates the use of adhesives according to the presentinvention to bond a metal to metal hem flange. An adhesive compositionwas prepared according to General Procedure B using the followingamounts of ingredients: LEVAPREN™ 70011V (44.5 parts), EPON™ 828 epoxyresin (44.5 parts), aluminum oxide (10.0 parts), CpXylFe⁺ SbF₆ ⁻ (1.0part).

Two pieces of 30.5 cm×10.1 cm cold rolled steel were bent to anglesappropriate for making a hem flange bond. For the piece that makes theinner part of the hem, 1.9 cm was bent up to an angle of about 45degrees. For the outer part of the hem, 1.3 cm was bent up pastperpendicular to an angle of about 120 degrees. Both bends were made torun the long way on the panel. Strips of the bulk adhesive were cut andpressed between silicone coated polyester release liner to about 0.38mm. Strips of tape (2.54 cm width) were cut from this for bonding. Thetape was exposed through the liner for three minutes on each side usingtwo 40 Watt 1.2 meter Super Diazo Blue Fluorescent lights (Philips TL40W/03) at a distance of about 10 cm.

The panels were prepared by wiping the bond area with Minnesota Miningand Manufacturing Company General Purpose Adhesive Cleaner No.-08984.The tape was then wrapped around the inner part of the hem so that thetape would bond to both the show-side of the outer panel and under thehem. The tape showed the right amount of tack and conformability to holditself to the metal and wrap easily around the edge. The inner panel wasinserted into the hem, which was pounded down tight against the innerpanel, completing the hem flange. The tape was cured using a heat gun,heating both sides of the bond along the entire length of the bond for atotal of about 15 minutes. The entire assembly was allowed to cool. Uponcooling, the adhesive squeeze out was inspected for indications of theextent of cure. The adhesive had hardened so that a thumb nail could notpenetrate it. This indicated that an adequate cure had been achieved.

Example 22

The adhesive composition of Example 20 was prepared according to GeneralProcedure B for the preparation of adhesives. After removal of thecomposition from the BRABENDER mixer, the material was stretched outinto a rope and allowed to cool to room temperature. Care was taken toavoid deleterious exposure of the material to ambient light, therebypreventing premature curing of the adhesive. A single screw extruderwith a 2.54 cm width adjustable ribbon die set at about 0.38 mm gap wasattached to the BRABENDER mixer. The rope of material was fed into theextruder, and the extrudate was wound around a core using a double sidedrelease liner. The tape was allowed to cool to room temperature and wasthen ready for use.

Other embodiments are within the following claims. While the inventionhas been described with reference to the particular embodiments anddrawings set forth above, the spirit of the invention is not so limitedand is defined by the appended claims.

What is claimed is:
 1. A curable composition formed by mixing componentscomprising:a) from about 30 to about 70 weight percent of a curableepoxy resin; b) from about 30 to about 70 weight percent of athermoplastic ethylene-vinyl acetate copolymer resin containing at least40 percent by weight vinyl acetate; and c) an effective amount of asulfonium or cationic organometallic salt photocatalyst for the curableepoxy resin, such that the total of components a) and b) is 100 weightpercent and wherein the composition is free from hydrocarbon polyolefinsand solvent and is a homogeneous mixture.
 2. The curable compositionaccording to claim 1 wherein said composition is a molten mixture. 3.The curable composition of claim 1 further comprising up to 50 percentby volume of one or more additives that alter the physicalcharacteristics of the resulting cured composition.
 4. The curablecomposition of claim 3 wherein the one or more additives comprisesaluminum oxide.
 5. The curable composition according to claim 1 whereinsaid composition is an unsupported film.
 6. The curable composition ofclaim 1 wherein said composition is an adhesive film used in a tape or aprotected film.
 7. The curable composition according to claim 6 providedin a roll construction.
 8. The curable composition according to claim 1wherein the photocatalyst is a cationic organometallic salt.
 9. Thecurable composition according to claim 10 wherein the cationicorganometallic salt is selected from the group consisting of (η⁶-xylenes (mixed isomers))(η⁵ -cyclopentadienyl)Fe⁺¹ SbF₆ ⁻, (η⁶ -xylenes(mixed isomers))(η⁵ -cyclopentadienyl)Fe⁺¹ PF₆ ⁻, (η⁶ -xylene)(η⁵-cyclopentadienyl)Fe⁺¹ SbF₆ ⁻, (η⁶ -mesitylene)(η⁵-cyclopentadienyl)Fe⁺¹ SbF₆ ⁻ and mixtures thereof.
 10. The curablecomposition according to claim 1 wherein said curable epoxy resincomprises at least one of an aliphatic, alicyclic, aromatic, andheterocyclic polyepoxide.
 11. The curable composition of claim 1 whereinsaid composition is bonded to a substrate and cured.
 12. The curedcomposition of claim 13 wherein said substrate is a metal or a polymer.13. The curable composition according to claim 6 wherein said tape isbonded to a substrate and cured.
 14. A curable composition comprising anhomogenous molten mixture containing:a) from about 40 to about 60 weightpercent of a curable epoxy resin; b) from about 40 to about 60 weightpercent of a thermoplastic ethylene-vinyl acetate copolymer resinwherein said copolymer contains at least 50 percent by weight vinylacetate; and c) an effective amount of an onium salt or a cationicorganometallic salt photocatalyst for the curable epoxy resin, such thatthe total of components a) and b) is 100 weight percent, the componentsa), b) and c) are a homogeneous mixture, and wherein the composition isfree from hydrocarbon polyolefins and solvent.
 15. The curablecomposition of claim 1 wherein the composition further comprises ahydroxyl-containing material for retarding the cure rate.